Labour MPs are clamouring for the Prime Minister to set a 'detailed timetable' for leaving Downing Street. Mr Blair could easily acquiesce. He could, for example, say he intends to stand down in January 2009. A general election isn't due until 2010, so Mr Blair would have honoured his twin promises not to stand again and to give his successor a chance to get to grips with the job. A year is ample time in politics.

But that would hardly satisfy the Labour ranks. Why not? Because talk of timetables is disingenuous. It is a veiled way of leaning on the Prime Minister to quit sooner rather than later. It is coded disloyalty.

Mr Blair has good reason to regret his pledge not to run for office again. It sapped his authority without neutralising the rebellion in his party. Learning from that example, he is right now to resist being specific about dates. His power would be terminated with immediate effect even if he gave several months' notice.

But it is quite unrealistic of Mr Blair to call, as he did last week, for an end to speculation about his future. Voters are entitled to wonder how long their Prime Minister plans to serve and to discuss who should replace him. Speculation of this sort is not the province of left-wing provocateurs. Nor, for that matter, is impatience for change. Opinion polls show Mr Blair's star is waning. Fatigue and disappointment with a long-serving leader is inevitable.

There is, however, a difference between speculation and agitation. By setting himself a term limit, the Prime Minister has made his intentions as clear as he can without fatally damaging his ability to govern. This was a big step towards compromise with his opponents in the party. They should reciprocate and stop trying to pester him out of office.

But the coalition ranged against Mr Blair has diverse motives. There is a hard core of backbenchers who resisted the party's move to electable territory as New Labour and who have conducted a rolling campaign of legislative sabotage ever since, continuing in opposition even while their party has been in government. But there is a much wider circle of less dogmatic MPs who are made nervous by a resurgent Tory party under a young and dynamic leader. They simply want an end to the current stalemate. They also worry that Mr Blair's distance from grass-roots members has hollowed out Labour's election-fighting machinery. Then there is the Chancellor and his allies who have artfully managed expectations so that a Gordon Brown premiership feels inevitable. They want a 'stable and orderly transition' of power, which means an uncontested succession.

Mr Brown has the most to gain from Mr Blair promptly vacating Number 10. The Chancellor is impatient to take a crown that he believes is his by right. But it is not. There is no reason why voters should automatically share Mr Brown's conviction that he is the best candidate for the top job. Opinion polls suggest he would not revive Labour's ratings.

The interests of the party and the country are, in fact, best served by Mr Blair sticking around. Even the most fervent Blair-baiters should recognise the opportunity presented to them by a Prime Minister who does not want to fight another election. Mr Blair is filling a caretaker role, allowing his party to conduct a debate about policy and the future direction of Labour. Whoever becomes the next leader will expect a quick return of discipline and will be grateful to Mr Blair for having absorbed so much of the party's venom. Labour should not ditch Mr Blair before it has agreed on how it wants to run the country.

But attacks on the Prime Minister are seldom accompanied by alternative policies. Last week, for example, the Prime Minister spoke of the need to intervene in families where children are at risk of growing up delinquent. Social services, he said, should have a more intrusive role earlier on in the lives of children at risk. That signals a drastic advance on Labour's already controversial approach to antisocial behaviour, using local government to re-engineer errant families.

This is an important area of policy affecting the lives of the poorest people in society. Presumably Labour MPs have a view. But the party refuses to be distracted from its covert campaign against the leader. What is the rebels' policy on antisocial behaviour? What, for that matter, is their policy on reforming the NHS and other public services? Or do they believe that public services need no reform, just more funds to be raised by higher taxes? Does Gordon Brown agree?

Tony Blair's statement of intent to stand down may have emboldened his opponents, but it has also called their policy bluff. The party needs to talk less about the current leader and more about what it will do once he has gone. Mr Blair, meanwhile, should use the fact that he does not face re-election to broach some unpopular but urgent subjects. He could make the case for road pricing to reduce congestion, for example. He could speak with conviction about the benefits for the UK of being a member of the EU. He could make the case for pension reforms that mean most people will have to work longer. He could also, without fear of being punished at the polls, acknowledge and reverse mistakes made during his time in office. He could, for example, return foreign languages to the national curriculum.

Why has Labour's internal policy debate been so muted? The short answer is because no one wants openly to challenge Gordon Brown's claim to be the next leader and Mr Brown himself is disinclined to make his views known. His preferred method for communicating policy views outside the economy is vague inference and anonymous briefing, as when five words about Britain's nuclear deterrent in a Mansion House speech were spun on to newspaper front pages as a dramatic intervention on the future of Trident. This cagey style is a shame since the Chancellor is reported privately to be a man of erudition and charm with a deep commitment to fighting poverty.

But Mr Brown's secretive tendency has alienated cabinet colleagues. He has kept jealous control of the agenda in departments that require disbursements from the Treasury, often refusing to enlighten even the Prime Minister about his plans. Perhaps the Chancellor would shed his carapace of inscrutability once the keys to Number 10 were finally his, but he might also bring to government a new level of centralising control and stubborn insularity. Mr Brown could feasibly beat David Cameron in an election based on his impressive record managing the economy. But only just. Labour must accept that this is not the same proposition as the 'renewal' for which its members are calling.

What, then, is the best course of action for Mr Blair and his party? The Prime Minister should continue in office for at least another year. Come spring 2007, in the run-up to local elections, around the time of his 10th anniversary in office, he should set in motion a contest for the succession to be run over the summer. He could do worse than copy Michael Howard, who gave Conservative leadership candidates sufficient room to debate policy and test themselves in the arena of public opinion. There is no doubt that David Cameron, who started that race as a rank outsider, was the best choice for his party. He rapidly turned its fortunes around.

Next year's Labour conference should be the scene for a dignified exit by Mr Blair and the installation of a leader with a clear programme and a democratic mandate earned in a poll of Labour members. The changes that the party craves will not be wrought by MPs harrying Tony Blair from Downing Street. Quite the contrary. Mr Blair must stay to allow a competitive race for a genuinely renewed leadership.